1. Field of the Invention
This invention relates to synthesis of organic aromatic materials and in particular to the synthesis of substituted styrenes.
2. Art Background
Styrene materials have been used in a wide variety of applications and have found particular usefulness as monomers for the production of polymers. A class of styrene materials, styrene monomers having alkoxycarbonyloxy (ACO) substituents, have recently undergone intensive investigation as precursors to polymers employed in applications such as coatings and lithography for device manufacture. For example, t-butoxycarbonyloxystyrene co- and homo-polymers have been used in the production of polymers employed for lithographic purposes, as described in U.S. Pat. No. 4,996,136 issued Feb. 26, 1991, and U.S. patent application Ser. No. 07/806,971 filed Dec. 12, 1991 (which are hereby incorporated by reference). Additionally, 4-hydroxystyrene copolymers formed from acetoxystyrenes in the presence of base have been suggested for uses such as corrosion protection. Such polymerization is exemplified in European Patent Application A2 0260104 published Mar. 16, 1988, and U.S. Pat. No. 4,689,371 published Aug. 25, 1987, where acetoxystyrene and a second substituted styrene are reacted in the presence of base and a free radical initiator at 145.degree. C. to form copolymers including hydroxystyrenes and other substituted styrene moieties.
Simple functionalization, e.g. esterification of the hydroxyl group in a hydroxystyrene starting material is generally very difficult due to the instability of such reactants. Therefore, styrene monomers with substituents have generally been made by first reacting materials such as di-tert-butyl dicarbonate with a hydroxyl substituted acylbenzene such as p-hydroxybenzaldehyde to form ##STR1## This intermediate is then reacted in the presence of a methylene Wittig reagent to form a styrene as exemplified in U.S. Pat. No. 4,491,628 Jan. 1, 1985. The process is expensive due to the cost of the Wittig reagent and due to the lower yields resulting from a multi-step procedure.
More recently, Allan E. Nader et al. have disclosed another method for synthesis of t-butoxycarbonyloxystyrene. This procedure starts from the generation of 4-hydroxystyrene using the aqueous base cleavage of 4-acetoxystyrene analogous to the same reaction of 4-vinylphenyl benzoate described by W. J. Dale et al., Journal of the American Chemical Society, 80, 3645 (1958), and also B. B. Corson et al., Journal of Organic Chemistry, 23, 544 (1958). This cleavage is followed by the phase transfer catalyzed t-butyloxycarbonylation of the phenolate derived from 4-hydroxystyrene as described by F. Houlihan et al., Canadian Journal of Chemistry, 63, 153 (1985). The resulting combination of steps affords high crude yields of t-butoxycarbonyloxystyrene. However, this material was, as is customary, purified by distillation and the yield of purified material after distillation is not reported.